discourse/app/assets/javascripts/discourse-common/lib/helpers.js.es6

import { get } from 'discourse-common/lib/raw-handlebars';

// `Ember.Helper` is only available in versions after 1.12
export function htmlHelper(fn) {
  if (Ember.Helper) {
    return Ember.Helper.helper(function(...args) {
      args = (args.length > 1) ? args[0].concat({ hash: args[args.length-1] }) : args;
      return new Handlebars.SafeString(fn.apply(this, args) || '');
    });
  } else {
    return Ember.Handlebars.makeBoundHelper(function() {
      return new Handlebars.SafeString(fn.apply(this, Array.prototype.slice.call(arguments)) || '');
    });
  }
}

const _helpers = {};

export function registerHelper(name, fn) {
  if (Ember.Helper) {
    _helpers[name] = Ember.Helper.helper(fn);
  } else {
    return Ember.HTMLBars._registerHelper(name, fn);
  }
}

export function findHelper(name) {
  return _helpers[name] || _helpers[name.dasherize()];
}

export function registerHelpers(registry) {
  Object.keys(_helpers).forEach(name => {
    registry.register(`helper:${name}`, _helpers[name], { singleton: false });
  });
}

function resolveParams(ctx, options) {
  let params = {};
  const hash = options.hash;

  if (hash) {
    if (options.hashTypes) {
      Object.keys(hash).forEach(function(k) {
        const type = options.hashTypes[k];
        if (type === "STRING" || type === "StringLiteral") {
          params[k] = hash[k];
        } else if (type === "ID" || type === "PathExpression") {
          params[k] = get(ctx, hash[k], options);
        }
      });
    } else {
      params = hash;
    }
  }
  return params;
}

export function registerUnbound(name, fn) {

  const func = function(property, options) {
    if (options.types && (options.types[0] === "ID" || options.types[0] === "PathExpression")) {
      property = get(this, property, options);
    }

    return fn.call(this, property, resolveParams(this, options));
  };

  if (Ember.Helper) {
    _helpers[name] = Ember.Helper.extend({
      compute: (params, args) => fn(params[0], args)
    });
    Handlebars.registerHelper(name, func);
    return;
  }

  Handlebars.registerHelper(name, func);
  Ember.Handlebars.registerHelper(name, func);
}